An optical fiber tends to be subject to bending, forces or stresses in applications. For example, fibers used for an optical network or fiber communication link, such as International Telecommunication Union recommended ITU-T G.652 single-mode optical fiber and cable, would suffer a fiber bend or stress loss which may adversely affect the performance or reliability of the fiber. Such fiber bending or stress could be measured by a commercial multiple-wavelength optical time domain reflectometer (OTDR), e.g. at 1310 nm or 1550 nm, to distinguish a bend loss from other losses, e.g. broken or connection loss, by use of the measured bend or stress induced loss difference information at different wavelengths. Such measurement is based on a bigger mode field diameter at a longer wavelength, thus for the most installed telecom optical fiber a bend or stress induced loss is higher at a longer wavelength, for example a bend loss at 1550 nm is bigger than that at 1310 nm.